In recent years, with the wide use of information equipments such as a personal computer, the population of a digital camera and a color printer, and the explosive increase of users of the Internet, the technique of a digital image has spread over daily life. The coding compression techniques such as JPEG (Joint Photographic Expert Group) and MPEG (Motion Picture Expert Group) are standardized for a static image and a video image, respectively.
On the other hand, the replaying technique of a recording media such as CD-ROM has been improved, and the convenience of the delivery and replaying of image data through transmission media such as a network or a broadcasting has been improved. As for the JPEG, JPEG 2000 as an evolution edition is released, and also goals in middle and long ranges of the MPEG are settled. In this way, it could be considered that the image processing technique for the information equipment could be further improved in future.
A conventional decoding method of the above JPEG 2000 is disclosed in Japanese Laid Open Patent Application (JP-P2002-325257A). FIG. 1 shows the structure of an image decoding apparatus 10 in this conventional example. This conventional image decoding apparatus 10 may be realized by a CPU, a memory, and other LSIs in hardware. Also, this conventional image decoding apparatus 10 may be realized by a program having an image decoding function in software. FIG. 1 is a schematic functional block diagram showing the image decoding apparatus realized through cooperation of them. Therefore, a person in the art could understand that the functional block can be realized by only the hardware, only the software or those combinations.
The above-mentioned image decoding apparatus 10 is composed of a decoding section 12 and a simplification section 30 mainly. The decoding unit 12 contains a stream analyzing section 14, an arithmetic decoding section 16, a bit modeling decoding section 18, an inverse quantization section 20 and an inverse wavelet transform section 24.
The stream analyzing section 14 receives and analyzes a compressed data (coded image data) CI, and the arithmetic decoding section 16 carries out an arithmetic decoding process to the coded image data CI based on the result of the analysis. The bit modeling decoding section 18 decodes the data obtained as the result of the arithmetic decoding process in the form of a bit plane for every color component, and the inverse quantization section 20 carries out an inverse quantization process to the decoding result by the bit modeling decoding section 18. The inverse wavelet transform section 24 carries out an inverse wavelet transform process to an image WIn of the n-th layer obtained as the result of the inverse quantization process. The inverse wavelet transform section 24 uses a frame buffer (not shown) as a work area. Finally, a decompressed image DI is outputted from the frame buffer.
On the other hand, the simplification section 30 contains a converting section 32, a time table 34 and a replay stop detecting section 36. The converting section 32 monitors the progress situation of the decoding process by the inverse wavelet transform section 24 and switches the decoding process to a simplifying process compulsorily, when the time exceeds a predetermined time limit. The time table 34 stores a time limit to be referred to by the converting section 32, and the replay stop detecting section 36 detects a fact that the user instructs the replay of the image to be stopped.
A frame which is being decoded and replayed when the user instructs suspension or end of the decoding or replaying operation is actually released from the time limit of the decoding process. Therefore, when the instruction of the suspension or end of the replaying operation is detected by the replay stop detecting section 36, the simplifying process to the frame by the converting section 32 is avoided and the replaying operation is fully carried out, like the usual manner. However, there is a case that the simplifying process by the converting section 32 has already begun. In such a case, the subsequent decoding process is carried out as usually as possible.
The converting section 32 refers to a clock signal CLK to measure the elapsed time. The clock signal CLK is frequency-divided in the converting section 32 according to necessity, and is counted by a counter (not shown) to measure a predetermined time. Also, the converting section 32 may refer to an externally provided time clock section such as a PIT (programmable interrupt timer) instead of the clock signal CLK. Also, in this example, the converting section 32 monitors the decoding process of the inverse wavelet transform section 24. However, it is not always necessary for the converting section 32 to monitor the decoding process of the inverse wavelet transform section 24. The elapsed time of either of the decoding processes from the stream analyzing section 14 to the inverse wavelet transform section 24 may be monitored.
As seen the above description, in the conventional image decoding apparatus, it is necessary to provide the converting section 32 to compulsively stop the decoding process for all or each of the decoding sections. Therefore, it is difficult to control the process time optimization of the whole system. Also, the converting section 32 compulsively stops the subsequent processes so that the control cannot be carried out accurately. As a result, it is difficult to suppress the degradation of image quality.